One method for preparing a difunctional telechelic prepolymer is uni-directional polymerization of an olefin from a monofunctional initiator that already carries a desired functional group, followed by coupling the growing chain ends. Thus, the uni-directional polymerization method requires a monofunctional initiator that also carries a desired functionality plus a suitable coupling agent to join the growing chain ends pairwise. A variation of this method is uni-directional polymerization of an olefin from a monofunctional initiator that already carries a desired functional group, followed either by in-situ quenching or post-polymerization modification. In many cases, especially for isobutylene, both the initiator, and the coupling agent, quenching agent, or post-polymerization functionalization chemistry are limitations to commercialization.
Another method for preparing a difunctional telechelic prepolymer is bi-directional polymerization of an olefin from a difunctional initiator, followed by functionalization of the growing chain ends, either by in-situ quenching or post-polymerization modification. Thus, the bi-directional polymerization method requires a difunctional initiator plus suitable functionalization chemistry to convert the growing chain ends to the desired functionality. In many cases, especially for isobutylene, the availability of a suitable difunctional initiator is a commercial limitation.
One additional method for preparing a difunctional telechelic prepolymer is constructive degradation. See, e.g., Ebdon et al. Macromol. Rep. 1995, A32, 603-611. When a high molecular weight copolymer of an olefin containing a small percentage of comonomer units is subjected to a cleavage reaction, for example, two new end groups with a desired functionality are created.
One example of constructive degradation is ozonolysis of main-chain double bonds that are introduced into a polymer by copolymerization of a diene or monosubstituted acetylene. See, e.g., Ebdon and Rimmer, J. Polym. Sci., Part A: Polym. Chem. 1997, 35, 3255-3262; Reyx and Campistron, Die Angew. Makromol. Chem. 1997, 247, 197-211. For example, the ozonolysis of butyl rubber yields a mixture of methyl ketone, aldehyde, and/or carboxylic acid end groups. See, e.g., Macias and Rubio, Revista de Plasticos Modernos 1978, 35, 604-611, 623; Beresnev and Yunusov, J. Appl. Chem. USSR 1991, 64, 2704-2707; U.S. Pat. Nos. 5,484,857 and 5,717,027. Those functional groups can be reduced to hydroxyl using LiAlH4. See, e.g., Macias and Rubio, Revista de Plasticos Modernos 1978, 35, 604-611, 623. Amine end groups can be obtained when butyl rubber is ozonolyzed in the presence of hexamethylenediamine. See, e.g., Beresnev and Yunusov, J. Appl. Chem. USSR 1991, 64, 2704-2707.
Another example of constructive degradation is metathesis degradation of polymers containing main-chain double bonds. For example, the metathesis reaction of poly(isobutylene-co-butadiene) (96.4/3.6, mol/mol) with 1,10-di(9-borabicyclononane)-5-decene yielded polyisobutylene oligomers carrying 9-borabicyclononane (9-BBN) end groups, which can then be oxidized to yield primary hydroxyl end groups. See, e.g., Chasmawala and Chung, Macromolecules 1995, 28, 1333-1339.
Suitable copolymers for constructive degradation are readily prepared from a monofunctional initiator and a suitable comonomer. The selection of monofunctional initiator is not critical, for example, simple compounds such as water or HCl are suitable initiators for isobutylene. Also, suitable comonomers such as isoprene are commercially available.
Functionalized polymers are useful intermediates in the preparation of high-performance polymer products. For example, polymers containing functional end groups are useful in the production of fuel or lube oil additives, network polymers, star-branched polymers, and block copolymers. Polymers containing primary aliphatic hydroxyl end groups are useful in polyurethane polymer synthesis. Polymers containing primary aliphatic halogen end groups are useful synthetic intermediates because the halogen group(s) can readily be converted into another group via nucleophilic substitution. Polymers containing phenol end groups are useful in the synthesis of fuel and lubricating oil additives because, for example, they are readily reacted with formaldehyde and a polyamine to generate ashless dispersants. Thus, there is a need for methods for preparing functionalized polymers.